An all-wheel drive driveline system for a motor vehicle generally comprises a primary front drive axle coupled to a secondary or rear drive axle.
When only two wheels of a four-wheel vehicle operate as driving wheel, the rear drive system including the rear drive axle and rear wheels may be disconnected from the front drive system including the front drive axle and front wheels. Furthermore, it could be desirable to disconnect only one of or both rear wheels depending on the operation mode of the motor vehicle.
For this purpose, it is known to provide a rear drive module to the rear drive system, the rear drive module including clutch thrust devices to distribute torque between the front and rear axle, and between the two wheels. Clutch thrust devices are also able to disconnect the rear drive system, the wheel being uncoupled to driveline. It is also known rear drive modules including two clutches, each of the clutches being able to disconnect one rear wheel from the driveline.
Such rear drive modules enable a motor vehicle with off-road capabilities, and on-road high performances, in particular with efficient stability, efficient dynamic operation, and also low fuel consumption.
Advantageously, the clutch thrust devices are of the well-known multi-plate types and include an axially movable piston disposed within a cavity between a clutch bearing and a housing, the piston cavity being connected to a source of hydraulic fluid which may variably provide pressurized fluid in the cavity to axially move the piston. Clutch thrust devices further include a resilient biasing member exerting an axial preload onto the clutch bearing. The clutch bearing is able to axially move by the piston movement and then actuates a coupling member engaging the plates. It is known to use a clutch bearing with a plurality of needles.
It is desirable to further improve the performances of such rear drive module, in particular by limiting the friction torque within the module and in particular in the clutch bearing to further reduce the vehicle fuel consumption.